Forking solution to https://www.hackerrank.com/challenges/bigger-is-greater

bigger-is-greater_v14.rb

#!/usr/bin/env ruby

# ehxxdsuhoowxpbxiwxjrhe  # Input
# ehxxdsuhoowxpbxiwxrehj  # Expected
# ehxxdsuhoowxpbxiwxehj
# ehxxdsuhoowxpebhijrwxx  # v2 output (jump, sort)
#              behijrwxx  # Sorted chars
#              123456788  # Numerals for testing
# 184785632  # Input
# 184786235  # Expected
# 213456788  # v2 output

fork_readers = []

input = (ARGV[0] && IO.read(ARGV[0]) || STDIN.read).split
(1..input.size-1).each_slice(10000) do |line_nums_for_fork|
  reader, writer = IO.pipe
  fork_readers << reader
  fork do
    reader.close
    answers = []
    for l in line_nums_for_fork do
      str_next = input[l].chars
      str_curr = [str_next.pop]
      loop do
        if str_next.size == 0
          answers << "no answer"
          break
        end
        str_curr.insert(0, str_next.pop)
        head_curr = str_curr[0]
        str_curr.sort!
        # Find the smallest character that is greater than the current most significant one
        head_next_idx = str_curr.index { |c| c > head_curr }
        next if !head_next_idx
        # Move it to the front
        head_next = str_curr[head_next_idx]
        str_curr.slice!(head_next_idx)
        answers << str_next.join + head_next + str_curr.join
        break
      end
    end
    # puts "Writing"
    writer.puts answers
  end # end forking
  writer.close
end

out = fork_readers.map(&:read)
Process.waitall
puts out